Position detecting device and position detecting method

ABSTRACT

A position detection method for detecting the position of marks comprises the following steps: a step for detecting first information relating to the position of the mark by detecting light from the mark under first measurement conditions; a step for detecting second information relating to the position of the mark by detecting light from the mark under second measurement conditions which differ from the first measurement conditions; and a step for detecting the position of the mark based on the first and second information, thereby providing a high-precision position detecting method and device serving as an alignment or overlaying detection device in an exposure apparatuses used in manufacturing semiconductor devices, wherein position detection precision is not lost even in the event that the alignment marks are not symmetrical or there are irregularities in the non-symmetry of multiple alignment marks within the same wafer.

BACKGROUND OF THE INVENTION

This application is a continuation of copending U.S. patent applicationSer. No. 11/190,168, filed Jul. 27, 2005. which is a continuation ofU.S. patent application Ser. No. 10/662,408 filed Sep. 16, 2003. andwhich issued as U.S. Pat. No. 6,999,893 on Feb. 14, 2006.

1. Field of the Invention

The present invention relates to a position detecting device and aposition detecting method, and, particularly, to a position detectingdevice and a position detecting method effective with regard to waferalignment in semiconductor exposure devices.

2. Description of the Related Art

Increasingly miniaturized and high-density circuits necessitate thatsemiconductor device manufacturing projection exposure apparatuses beable to project circuit patterns on reticles onto wafer surfaces forexposure at even higher resolution. The projection resolution of acircuit pattern depends on the apertures (NA) of the projection opticalsystem and on the exposing light wavelength, so methods are beingemployed for raising the resolution, such as increasing the NA of theprojection optical system or using light having a shorter wavelength forexposure. With regard to the latter, the exposure light source has madea transition from g rays to i rays, and from i rays to the excimerlaser. Exposure devices using an excimer laser with an oscillationwavelength of 248 nm and 193 nm are already in practical use.

Currently, even shorter wavelength VUV exposure using a wavelength of157 nm, and EUV exposure using a wavelength of around 13 nm, are beingstudied as candidates for next-generation exposure.

Also, there is an increasing variety in semiconductor devicemanufacturing processes, and CMP (Chemical Mechanical Polishing)processes and the like are being introduced as smoothing techniques toresolve the problem of insufficient depth of the exposure apparatus.

Also, there is a great variety of structures and materials for thesemiconductor devices, with the P-HEMT (Pseudomorphic High ElectronMobility Transistor) and M-HEMT (Metamorphe-HEMT) made up of acombination of compounds, such as GaAs or InP, or the like, and HBT(Heterojunction Bipolar Transistor) using SiGe or SiGeC, or the like,for example, being proposed.

On the other hand, increased miniaturization of the circuit patternmeans that highly-precise alignment between the reticle upon which thecircuit pattern is formed and the wafer upon which the pattern is castis accordingly necessary. The required precision is ⅓ of the circuitline width, so with a current design using 180 nm, for example, therequired precision is 60 nm.

Alignment in an exposure apparatus is performed by exposure transferringof alignment marks on the wafer at the same time as the circuit patternon the reticle, optically detecting the position of the alignment marksat the time of exposing the circuit pattern of the next reticle on thewafer, and positioning the wafer as to the reticle. Techniques fordetecting the alignment include a method wherein the alignment marks areenlarged and taken with a microscope so as to detect the position of themark image, a method wherein a diffraction grating is used as alignmentmarks so as to detect the phase of interference signals frominterference with the diffraction light therefrom, thereby detecting theposition of the diffraction grating, and so forth.

In the current situation of the semiconductor industry, as describedabove, improving the precision of overlaying on device wafers at thetime of using exposure apparatuses is an issue, which is crucial inimproving the capabilities of the semiconductor devices and improvingproduction yield. However, the fact is that while circuit patterns canbe configured well due to introduction of special semiconductormanufacturing techniques such as CMP processing and the like, butirregularities in alignment mark shape occur from one wafer to anotheror from one shot to another, resulting in non-symmetric alignmentmark-structures, frequently bringing about deterioration in thealignment precision.

The cause of non-symmetric alignment mark structures can be attributedto an increased difference between the line width of the circuit patternand the line width of the alignment mark, due to increasinglyminiaturized circuit patterns. The process conditions for filmformation, etching, CMP, etc., are optimized for the line width of thecircuit patterns (a line width of 0.1 to 0.15 μm), so structures with aline width in generally the same order do not become non-symmetric, butthe alignment marks with a large line width in comparison with thecircuit patterns (a line width of 0.6 to 4.0 μm) do not match theoptimal process conditions, and accordingly, may turn out beingnon-symmetric. Attempting to match the line width of the alignment markswith the line width of the circuit patterns results in the signalintensity or contrast deteriorating due to insufficient resolution ofthe detection optical system used for alignment, leading to poorerstability in alignment signals. A detection optical system capable ofdetecting alignment marks with the same line width as the circuitpatterns would require an alignment light source with a large NA and ashort wavelength, which is a detection optical system on the same levelas with the projection optical system, leading to a new problem ofincreased costs for the apparatus.

Currently, this issue is being dealt with by changing the processconditions by trial and error so as to be suitable for both thealignment marks and circuit patterns, or to make several types ofalignment mark line widths for exposure evaluation, and use thealignment marks with the best line width.

Accordingly, this has required great amounts of time for determiningoptimal conditions (parameters). Also, even after parameters aredetermined, in the event that a process error, or the like, occurs,there is the need to change the parameters for the manufacturingapparatus accordingly, with the changes in the manufacturing process,which requires a great amount of time again. Moreover, even moreminiaturized circuit patterns, new semiconductor processes, 300 mmwafers, and so forth, are expected to make manufacturing with no defectson the whole surface of a wafer in both the circuit patterns andalignment marks even more difficult.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above-describedpresent state, and accordingly, it is an object of the present inventionto achieve a high-precision position detecting method and positiondetecting device to serve as an alignment or overlaying detection devicein an exposure apparatuses used in manufacturing semiconductor devices,wherein position detection precision is not lost even in the event thatthe alignment marks to be used are not symmetric, or further in theevent that there are irregularities in the non-symmetry of multiplealignment marks within the same wafer.

The position detection method for detecting the position of marksaccording to the present invention comprises the following steps: a stepfor detecting first information relating to the position of the mark bydetecting light from the mark under first measurement conditions; a stepfor detecting second information relating to the position of the mark bydetecting light from the mark under second measurement conditions, whichdiffer from the first measurement conditions; and a step for detectingthe position of the mark based on the first and second information.

Due to such an arrangement, even in the event that there areirregularities in the non-symmetry of alignment marks from one shot toanother or from one wafer to another at the time of executing globalalignment, the measurement error due to the non-symmetry can becorrected based on measurement values measured under two differentconditions, so measurement is not readily affected by structural changeof the alignment marks due to the semiconductor processes, alignmentprecision can be improved, and yield in the semiconductor devicemanufacturing process can be improved. Further, the time for calculatingthe conditions for the semiconductor process which has been necessary inorder to stabilize the shape of the alignment marks so far can bereduced, thereby improving the productivity of semiconductor devicemanufacturing, as well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an embodiment of a management systemfor a semiconductor exposure apparatus according to the presentinvention.

FIG. 2 is a diagram illustrating an alignment scope according to thepresent invention.

FIG. 3 is a diagram illustrating a first example of alignment marksaccording to the present invention.

FIG. 4 is a diagram illustrating a second example of alignment marksaccording to the present invention.

FIG. 5 is a diagram illustrating an example of alignment signals.

FIGS. 6A through 6C are diagrams illustrating a template matching methodaccording to a first embodiment of the present invention.

FIG. 7 is a diagram describing global alignment.

FIG. 8 is a diagram illustrating linear coordinates conversion andcorrection residual.

FIG. 9 is a non-symmetric mark model used for describing the firstembodiment according to the present invention.

FIG. 10 is a diagram illustrating the relation between non-symmetry ofmarks and measurement error with the first embodiment according to thepresent invention.

FIG. 11 is a diagram describing the relation between alignmentmeasurement values and overlaying detection device measurement values,and measurement error.

FIG. 12 is a diagram illustrating a method for calculating non-symmetricerror correction values.

FIG. 13 is a diagram illustrating the alignment sequence of the presentinvention.

FIG. 14 is a diagram illustrating a second signal processing methodaccording to the present invention.

FIG. 15 is a diagram illustrating the relation between non-symmetry ofmarks and measurement error with a second embodiment according to thepresent invention.

FIG. 16 is a diagram illustrating the alignment detection system of thesecond embodiment according to the present invention.

FIG. 17 is a diagram illustrating the relation between non-symmetry ofmarks and measurement error with a third embodiment according to thepresent invention.

FIG. 18 is a diagram illustrating the alignment detection system of thethird embodiment according to the present invention.

FIG. 19 is a non-symmetric mark model used for describing a fourthembodiment according to the present invention.

FIG. 20 is a diagram illustrating the relation between non-symmetry ofmarks and measurement error with the fourth embodiment according to thepresent invention.

FIG. 21 is a diagram illustrating the alignment detection system of thefourth embodiment according to the present invention.

FIG. 22 is a non-symmetric mark model used for describing a fifthembodiment according to the present invention.

FIG. 23 is a diagram illustrating the relation between non-symmetry ofmarks and measurement error with the fifth embodiment according to thepresent invention.

FIG. 24 is a diagram illustrating the alignment detection system of thefifth embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of preferred embodiments of the presentinvention with reference to the attached drawings.

First Embodiment

FIG. 1 is a schematic diagram of a semiconductor exposure apparatusaccording to the present invention. Note that only the portionsnecessary for describing the embodiments are shown, and the otherportions are omitted in the drawings. The exposure apparatus 1 isconfigured of a reduction projection optical system 11 for reducedprojection of a reticle 10 upon which a circuit pattern has been drawn,a wafer chuck 13 for holding a wafer 12 upon which a base pattern andalignment marks have been formed in previous processes, a wafer stage 14for positioning the wafer 12 to a predetermined position, an alignmentdetection optical system 15 for measuring the position of the alignmentmarks on the wafer, and so forth.

Next, the principle of alignment detection will be described. FIG. 2illustrates the principal components of the alignment detection opticalsystem 15. FIG. 2 is an example of an optical system for detectingposition in the x direction, and a description of the x-directionaldetection system will be made, since y-directional detection can beperformed by a system rotated 90° on the z axis (x-directional markswhich are rotated 90° on the z axis are used for the y-directionalmarks, as well). The alignment detection optical system 15 is configuredof an illumination system 15 i and an imaging system 15 o.

Illumination light from a light source 18 is enlarged at a lens 19 tobecome parallel rays, and then is condensed again at a lens 22. Thecoherency (σ) of the illumination light is adjusted by a variableopening diaphragm 20. An aperture 23 is disposed at a position conjugatewith the wafer 12, and serves as a view field aperture to preventunnecessary light from being cast on the surrounding areas of thealignment marks on the wafer 12. The light collected by the lens 22 isformed into parallel rays again at the lens 24, reflected at a beamsplitter 25, passes through a lens 26, and illuminates an alignment mark50 on the wafer 12. The reflected light from the alignment mark 50passes through the lens 26, beam splitter 25, lenses 27 and 28, is splitat the beam splitter 30, and is received at line sensors 32 and 34. Theaperture (NA) of the imaging system can be adjusted by the variableopening diaphragm 29. The alignment mark 50 is enlarged at an imagingmagnification of around one hundred times, and is imaged at the linesensor 32. On the other hand, the image received at the line sensor 34is situated at a position intentionally offset from the best focusposition in the direction of the optical axis, so that the line sensor34 can detect signals of a defocused image while the line sensor 32detects the best focus image signals. Two-dimensional area sensors canalso be used for the sensors 32 and 34.

As for the alignment mark 50, marks having a shape such as shown inFIGS. 3 or 4 are used. In FIG. 3, four rectangular marks, which are 4 μmin the X directions which is the measurement direction, and 20 μm in theY direction, which is the non-measurement direction, are arrayed at a 20μm pitch. The mark portion has a recessed cross-sectional form, since itis formed by etching. While resist is applied to the mark portion inreal cases, this is not shown in the drawings. On the other hand, thearrangement shown in FIG. 4 has the outline portions of the marks shownin FIG. 3 substituted by 0.6 μm wide lines. Whichever of the alignmentmarks in FIGS. 3 and 4 is used, the image taken by the line sensors 32and 34 is as shown in FIG. 5, due to scattered light at the edgeportions at angles too great to enter the NA of the lens of thealignment detection system 15, and interference with the scattered lightat the edge portion. The outlines of the alignment marks shown in FIG. 3are dark, and the recesses of the alignment marks shown in FIG. 4 aredark or bright. This is an image often observed in bright field images,and is characteristic thereof.

Now, the alignment mark image taken in this way is processed withalignment signal processing means 16 as described below. Templatematching is used for calculating the alignment mark position used withthe present embodiment. With template matching, correlation computationis performed between the obtained signals, which are indicated by S inFIG. 6B and the template T shown in FIG. 6A, which the apparatus hasbeforehand, wherein the position with the highest correlation isdetected as the center of the positioning mark. In the correlation valuefunction indicated by E in FIG. 6C, resolution of 1/10 to 1/50 pixelscan be achieved by obtaining the center-of-gravity pixel position of anarea of several pixels in the horizontal direction from the peak pixel.Template matching is expressed by the following Expression.[Expression 1] $\begin{matrix}{{E(X)} = \frac{1}{\sum\limits_{J = k}^{k}\left\lbrack {{S\left( {X + J} \right)} - {T(J)}} \right\rbrack^{2}}} & (1)\end{matrix}$wherein S represents signals obtained with the sensor, T represents thetemplate, and E represents the correlation results.

FIGS. 6A through 6C show the method for processing one of the fouralignment mark images. The position of the other three alignment markimages on the sensor are detected by template matching, as well. Thetemplate matching yields the mark image positions X1(n), X2(n), X3(n),and X4(n), in increments of pixels, wherein n represents the templatenumber.

Subsequently, the average position of the marks is obtained by

[Expression 2]Xa(n)=[X1(n)+X2(n)+X3(n)+X4(n)]/4.  (2)

The positional offset Xw(n) of the alignment mark 50 on the waferobtained for each template can be obtained as

[Expression 3]Xw(n)=Xa(n)/(Px.M)  (3)wherein M represents the imaging magnification of the alignment scope 15and Px represents the pixel pitch of the alignment measurement directionof the area sensor 23. The positional offset amount X1 of the alignmentmark from the best focus image signals obtained from the line sensor 32and the positional offset amount X2 of the alignment mark from the linesensor 34 are obtained based on Expression (3).

The alignment mark position X is determined using these two positionoffset measurement values. The processing method thereof will bedescribed later in detail.

Next, the method for aligning the wafer based on the positionmeasurement values of the alignment mark will be described. The presentembodiment uses global alignment known as AGA (Advanced GlobalAlignment). With global alignment, several shots of all of the chips(shots) on the wafer are selected (the selected shots are called “sampleshots”), and the positions of the alignment marks within the shots aredetected.

FIG. 7 illustrates the way in which the shots on the wafer are arrayedwith regard to the x-y coordinates system on the wafer stage of theexposure apparatus 1. Wafer offset can be described by the sixparameters of x-directional shift Sx, y-directional shift Sy,inclination θx as to the x axis, inclination θy as to the y axis,x-directional magnification Bx, and y-directional magnification By. Bxand By represents the expansion of shrinkage of the wafer with waferstage feeding by the exposure apparatus as a reference, a phenomenonwhich occurs due to heating the wafer for film formation, etching, andso forth, in the semiconductor processes.

Now, the measurement value of the sample shots for AGA measuredaccording to the above-described method is described as Ai (wherein irepresents the measurement shot No.), as shown in the followingExpression.[Expression 4] $\begin{matrix}{{A\quad i} = \begin{pmatrix}{x\quad i} \\{y\quad i}\end{pmatrix}} & (4)\end{matrix}$

Also, the alignment mark design position coordinates of the sample shotare described as Di, as shown in the following Expression.[Expression 5] $\begin{matrix}{{D\quad i} = \begin{pmatrix}{X\quad i} \\{Y\quad i}\end{pmatrix}} & (5)\end{matrix}$

With AGA, the following linear coordinates conversion D′i is carried outusing the six parameters (Sx, Sy, θx, θy, Bx, By) describing thepositional offset of the wafer as described above.[Expression 6] $\begin{matrix}{{D^{\prime}i} = {{\begin{pmatrix}{B\quad x} & {{- \theta}\quad y} \\{\theta\quad x} & {B\quad y}\end{pmatrix}D\quad i} + \begin{pmatrix}{S\quad x} \\{S\quad y}\end{pmatrix}}} & (6)\end{matrix}$

In this expression, approximations such as cos θ=1, sin θ=θ, θx*Bx=θx,θy*By=θy, and so forth, are used for simplification, since θx, θy, Bx,and By are minute values.

FIG. 8 illustrates the way in which the linear coordinates conversionshown in Expression (6) is carried out. An alignment mark on the waferis at a position indicated by W, offset by an amount Ai from thedesigned position M, and performing the coordinates conversion D′ichanges the positional offset (residual) of the alignment mark on thewafer to Ri.

[Expression 7]Ri=(Di+Ai)−D′i  (7)

With AGA, the least-square method is used so that the residual Ri isminimal for each sample shot. That is to say, Sx, Sy, θx, θy, Bx, and Byare calculated such that the mean square sum of the residual Ri isminimal.[Expression 8] $\begin{matrix}\begin{matrix}{V = {\frac{1}{n}{\sum\limits_{i = n}{{R\quad i}}^{2}}}} \\{= {\frac{1}{n}{\sum\limits_{i = 1}{{\begin{pmatrix}{x\quad i} \\{y\quad i}\end{pmatrix} - {\begin{pmatrix}{{B\quad x} - 1} & {{- \theta}\quad y} \\{\theta\quad x} & {{B\quad y} - 1}\end{pmatrix}\begin{pmatrix}{X\quad i} \\{Y\quad i}\end{pmatrix}} + \begin{pmatrix}{S\quad x} \\{S\quad y}\end{pmatrix}}}^{2}}}}\end{matrix} & (8)\end{matrix}$[Expression 9] $\begin{matrix}{\begin{pmatrix}{\delta\quad{V/\delta}\quad S\quad x} \\{\delta\quad{V/\delta}\quad S\quad y} \\{\delta\quad{V/\delta}\quad\theta\quad x} \\{\delta\quad{V/\delta}\quad\theta\quad y} \\{\delta\quad{V/\delta}\quad B\quad x} \\{\delta\quad{V/\delta}\quad B\quad y}\end{pmatrix} = 0} & (9)\end{matrix}$

The measured values (xi, yi) at each sample shot and the alignment markdesign positions (Xi, Yi) are substituted in the Expressions 8 and 9 toobtain the AGA parameters (Sx, Sy, θx, θy, Bx, By), and positioning foreach of the shots on the wafer 12 is performed based on the AGAparameters, following which exposing is performed.

Next, the change in the positional offset measurement values of the bestfocus signals and defocus signals in the event that there isnon-symmetric error in the shape of the alignment mark 50 will bedescribed. FIG. 9 shows a cross-sectional shape model of an alignmentmark. With regard to a case wherein there is a difference in the angleof the inclination angle of the left side wall (P1-P2) and the angle ofthe inclination angle of the right side wall (P3-P4), first, thealignment image is calculated, following which the calculated error εfrom the center position of P2 and P3 is calculated with regard to thebest focus signals and defocus signals using template matching withExpression (3), the results of which are shown in FIG. 10. Theconditions of the alignment detection optical system are: aperture(NA)=0.4, σ=0.9, and TE polarization light for the illumination lightwith a wavelength of 633 nm from a He-Ne laser (with the electricalfield direction perpendicular to the drawing). The calculation resultsare for a case wherein the face of the wafer 12 is defocused by 1.5 μmfrom the best focus position. As shown in FIG. 10, the measurement errorincreases in proportion to the difference in angle between the left andright walls, and further, with the best focus signals and defocussignals, there is a difference between the rate of change in measurementerror regarding a change of the difference in angle between the left andright walls.

Thus, a crucial point of the present embodiment is that the sensitivityof change in measurement regarding non-symmetry of marks differs betweentwo measurement conditions. That is to say, the present embodiment takesadvantage of the fact that the difference value of offset amountsmeasured under two measurement conditions is zero with highlysymmetrical marks, but proportionately increases with an increase innon-symmetry thereof. With the measurement value of the firstmeasurement condition (best focus signal) as M1 and the measurementvalue of the second measurement condition (defocus signal) as M2, M,which indicates the true positional offset (the amount of offset at themidpoint between P2 and P3 in FIG. 9), can be expressed by

[Expression 10]M=M1−α.(M 1−M2)  (10)wherein α is a non-symmetry error correction coefficient.

Next, the method for obtaining this non-symmetry error correctioncoefficient α will be described. A first method is to measure eachsample shot under the first measurement conditions and secondmeasurement conditions at the time of the above-described AGA (globalalignment), store the measurement values and residual Ri for each shot,substitute the measured values (xi, yi) measured under the firstmeasurement conditions at each sample shot and the alignment mark designpositions (Xi, Yi) in the Expressions 8 and 9 to obtain the AGAparameters (Sx, Sy, θx, θy, Bx, By), and position each of the shots onthe wafer 12 based on the AGA parameters, following which exposure isperformed. At this time, a first overlaying evaluation mark is formed onthe wafer 12 along with the alignment mark 50, and a second overlayingevaluation mark on the reticle 10 is transferred by exposure onto theresist on the first overlaying evaluation mark following AGA alignment.The positional offset amount of the first and second overlayingevaluation marks is measured for a sample shot for the AGA using anoverlaying precision evaluation device. FIG. 11 shows the relation ofthese measurement values. The correction residual Ri (wherein i is theshot No.) measured by AGA and the measurement value Ki (wherein i is theshot No.) measured by the overlaying precision evaluation device shouldmatch with opposite signs, but in the event that there is non-symmetryin the alignment mark, these do not match by an error component εi dueto the non-symmetry. The error component εi can be obtained by εi=Ri+Ki(wherein i is the shot No.). Next, the relation between the errorcomponent εi, and the difference value dMi (i.e., M1i−M2i) of themeasurement value M1i under the first measurement conditions and themeasurement value M2i under the second measurement conditions, isobtained. FIG. 12 illustrates the correlation of the values of dMi andεi for each shot and an approximation line obtained by the least-squaremethod. Thus, an approximation line is obtained by the least-squaremethod from the difference value (M1i−M2i) and the error component(Ri+Ki), and the inclination thereof is denoted by α. This methoddetermines the value of the correction coefficient a based on theoverlaying precision evaluation device. Also, those skilled in the artwill be able to readily apply methods other than using an overlayingprecision evaluation device, such as a method for obtaining the offsetamount Ki following exposure based on electrical properties calledelectrical measurement, a method for obtaining Ki using a measuring SEM,and so forth.

Now, while a method has been described for obtaining the correctioncoefficient α, wherein exposure is performed following alignment, andthe exposed wafer is inspected with an inspecting device, such as anoverlaying precision evaluation device serving as a reference, anarrangement may be made wherein α is obtained such that the residual Riof the AGA is minimal. That is, an arbitrary value is set for thecorrection coefficient α, the alignment mark positional offset amountsof each shot are set with Expression (10) and substituted intoExpressions (8) and (9) to obtain the AGA parameters (Sx, Sy, θx, θy,Bx, By), the correction residual Ri is obtained with Expression (7), andthe standard deviation (σ) is obtained (or, this may be the maximalvalue). The value of the correction coefficient is changed and the sameprocessing is repeated, thereby obtaining a value wherein the residualRi is minimal.

The reason that the combination wherein the residual is the smallest isused is that the residual amount is the sum of non-linear distortioncaused by semiconductor processes and alignment measurement error (thesum of alignment precision and wafer state array precision), and thenon-linear distortion is constant within the same wafer, so the smallerthe residual is, the better the alignment measurement precision is.Also, an arrangement may be made wherein the above-described two methodsare combined to determine the correction coefficient α for a first waferin a semiconductor manufacturing lot (or the first several wafersthereof) using an overlaying precision evaluation device, or the like,so that the correction coefficient only needs to be fine-tuned from thenext wafer on such that the residual R is minimal at a value near thevalue α of the leading wafer.

Next, the alignment sequence of the present invention will be describedwith reference to the flowchart shown in FIG. 13. In Step 50, which shoton the wafer is to be used for the AGA measurement shot is set. In thefollowing Step 51, the value of the correction coefficient α determinedas described above is set. In Step 52, the alignment mark within thesample shot on the wafer mounted on the wafer stage is positioned underthe alignment detection system. In Step 53, an image of the alignmentmark is obtained by the alignment detection system under the firstmeasurement conditions. In Step 54, the positional offset amount M1 iscalculated from the obtained alignment mark image, and stored in theexposure apparatus. In Step 55, an image of the alignment mark isobtained by the alignment detection system under the second measurementconditions. In Step 56, the positional offset amount M2 is calculatedfrom the obtained alignment mark image, and stored in the exposureapparatus. Next, in Step 57, judgment is made regarding whether or notthere are sample shots to be measured based on the information in Step50, and in the event that there still are sample shots to be measuredthe flow returns to Step 52, so that measurement and signal processingis performed for all sample shots.

In Step 58, the mark offset amount Mi is obtained (wherein i is the shotNo.), using the correction coefficient a set in Step 51, and themeasurement value M1 obtained in Step 54 under the first measurementconditions and the measurement value M2 obtained in Step 56 under thesecond measurement conditions, by the expressionMi=M1i−α(M1I−M2i).

The wafer is positioned as to the exposure system based on the AGAmeasurement values calculated in Step 59, and the pattern on the reticleis transferred by exposure onto the wafer in Step 60.

Also, the following method can be used as processing for obtaining theposition of the alignment mark image as well, besides theabove-described template matching method. FIG. 14 illustrates a partialenlargement of the alignment mark image shown in FIG. 5, wherein theleft half of the signal is a reflected template.[Expression 11] $\begin{matrix}{{E(x)} = \frac{1}{\sum\limits_{J = a}^{b}{{{S\left( {X - J} \right)} - {S\left( {X + J} \right)}}}}} & (11)\end{matrix}$

Expression (11) is the correlation value, taking the left half of thesignal waveform to be a template. The position with the highestcorrelation is detected as the center of the positioning mark. With thiscorrelation value function, resolution of 1/10 to 1/50 pixels can beachieved by obtaining the center-of-gravity pixel position of an area ofseveral pixels in the horizontal direction from the peak pixel. Theposition of the other three alignment mark images on the sensor aredetected as well. Subsequently, the average position Xa(n) of the marksis obtained by Expression (2), and the positional offset Xw(n) of thealignment mark 50 on the wafer is obtained by Expression (3).

Second Embodiment

Next, a second embodiment of the present invention will be described.While the first embodiment involved using best focus signals and defocussignals as two measurement conditions, the present embodiment is anexample of a method wherein illumination light systems with differentcoherency (σ) are used to change sensitivity regarding non-symmetry ofthe alignment mark.

FIG. 15 illustrates the simulation results serving as a basis for thismethod. FIG. 9 shows the cross-sectional shape model of an alignmentmark, and, in the present embodiment, with regard to a case whereinthere is a difference in the angle of the inclination angle of the leftside wall (P1-P2) and the angle of the inclination angle of the rightside wall (P3-P4), first, the alignment mark image is calculated,following which the positional offset amount ε from the center positionof P2 and P3 is calculated with regard to differing coherency usingtemplate matching with Expression (3), the results of which are shown inFIG. 15. The conditions of the alignment detection optical system are:aperture (NA)=0.4, best focus, and TE polarization light for theillumination light with a wavelength of 633 nm from a He-Ne laser (withthe electrical field direction perpendicular to the drawing). Thecalculation results are for σ=0.9 and σ=0.2. As shown in FIG. 15, withσ=0.9 signals and σ=0.2 signals, there is a difference between the rateof change in measurement error regarding a change of the difference inangle between the left and right walls. With the measurement value ofthe first measurement condition (σ=0.9) as M1 and the measurement valueof the second measurement condition (σ=0.2) as M2, the true positionaloffset amount can be obtained by Expression (10).

The exposure apparatus according to the present embodiment is as shownin FIG. 1, but the alignment detection system 15 differs from thatdescribed in the first embodiment, so the configuration of the alignmentdetection system will be described here. FIG. 16 illustrates theprincipal components of the alignment detection system used in thepresent embodiment. The alignment detection optical system 15 isconfigured of an illumination system 15 i and an imaging system 15 o,wherein illumination light from a light source 18 is enlarged at a lens19 to become parallel rays, and then is collected again at a lens 22.The coherency (σ) of the illumination light is adjusted by a variableopening diaphragm 20. An aperture 23 is disposed at a position conjugatewith the wafer 12, and serves as a view field aperture to preventunnecessary light from being cast on the surrounding areas of thealignment marks on the wafer 12. The light collected by the lens 22 isformed into parallel rays again at the lens 24, reflected at a beamsplitter 25, passes through a lens 26, and illuminates an alignment markS0 on the wafer 12. The reflected light from the alignment mark 50passes through the lens 26, beam splitter 25, lenses 27 and 28, and isreceived at a line sensor 32. The aperture (NA) of the imaging systemcan be adjusted by the variable opening diaphragm 29. The alignment mark50 is enlarged at an imaging magnification of around one hundred times,and is imaged at the line sensor 32. Sequentially switching thecoherency (cy) of the illumination light between 0.9 and 0.2 with thevariable opening diaphragm 20 allows signals from the first measurementconditions, i.e., σ=0.9, and signals from the second measurementconditions, i.e., σ=0.2, to be obtained at the line sensor 32.

Note that the method for determining the correction coefficient α andthe AGA (global alignment) method are the same as those with the firstembodiment, and, accordingly, a description thereof will be omittedhere.

Third Embodiment

Next, a third embodiment of the present invention will be described. Thepresent embodiment is an example of a method wherein imaging systemswith different apertures (NA) are used to change sensitivity regardingnon-symmetry of the alignment mark.

FIG. 17 illustrates the simulation results serving as a basis for thismethod. FIG. 9 shows the cross-sectional shape model of an alignmentmark, and in the present embodiment, with regard to a case wherein thereis a difference in the angle of the inclination angle of the left sidewall (P1-P2) and the angle of the inclination angle of the right sidewall (P3-P4), first, the alignment mark image is calculated, followingwhich the positional offset amount ε from the center position of P2 andP3 is calculated with regard to differing aperture signals usingtemplate matching with Expression (3), the results of which are shown inFIG. 17. The conditions of the alignment detection optical system are:σ=0.9, best focus, and TE polarization light for the illumination lightwith a wavelength of 633 nm from a He-Ne laser (with the electricalfield direction perpendicular to the drawing). The calculation resultsare for aperture (NA)=0.4, and aperture (NA)=0.6. As shown in FIG. 17,with NA=0.4 signals and NA=0.6 signals, there is a difference betweenthe rate of change in measurement error regarding a change of thedifference in angle between the left and right walls. With themeasurement value of the first measurement condition (NA=0.4) as M1 andthe measurement value of the second measurement condition (NA=0.6) asM2, the true positional offset amount can be obtained by Expression(10).

The exposure apparatus according to the present embodiment is as shownin FIG. 1, but the alignment detection system 15 differs from thatdescribed in the first embodiment, so the configuration of the alignmentdetection system will be described here. FIG. 18 illustrates theprincipal components of the alignment detection system used in thepresent embodiment. The alignment detection optical system 15 isconfigured of an illumination system 15 i and an imaging system 15 o,wherein illumination light from a light source 18 is enlarged at a lens19 to become parallel rays, and then is collected again at a lens 22.The coherency (σ) of the illumination light is adjusted by a variableopening diaphragm 20. An aperture 23 is disposed at a position conjugatewith the wafer 12, and serves as a view field aperture to preventunnecessary light from being cast on the surrounding areas of thealignment marks on the wafer 12. The light collected by the lens 22 isformed into parallel rays again at the lens 24, reflected at a beamsplitter 25, passes through a lens 26, and illuminates an alignment mark50 on the wafer 12. The reflected light from the alignment mark 50passes through the lens 26, beam splitter 25, lenses 27 and 28, is splitat the beam splitter 30, and is received at line sensors 32 and 34. Theaperture (NA) of the imaging system can be adjusted by variable openingdiaphragms 29 and 35. The alignment mark 50 is enlarged at an imagingmagnification of around one hundred times, and is imaged at the linesensor 32 as NA 0.6 signals. On the other hand, the image received bythe line sensor 34 can be detected as NA 0.4 signals due to the variableopening diaphragm 35.

Note that the method for determining the correction coefficient α andthe AGA (global alignment) method are the same as those with the firstembodiment, and, accordingly, a description thereof will be omittedhere.

Fourth Embodiment

Next, a fourth embodiment of the present invention will be described.The present embodiment is an example of a method wherein illuminationsystems with different polarization are used to change sensitivityregarding non-symmetry of the alignment mark.

FIG. 19 shows the cross-sectional shape model of an alignment mark. Thealignment mark is such as shown in FIG. 4, and FIG. 20 illustrates theresults obtained using template matching with Expression (3), withregard to signals of light cast in with different polarization, in acase wherein there is an inclination at the bottom (base face) of themark. Here, first, the alignment mark image is calculated, followingwhich the calculated error ε is calculated with regard to differingpolarization signals using template matching with Expression (3), theresults of which are shown in FIG. 20. The conditions of the alignmentdetection optical system are: NA=0.4, σ=0.9, best focus, and wavelengthof 633 nm from a He-Ne laser. The calculation results are for TEpolarization (with the electrical field direction perpendicular to thedrawing), and TM polarization, for the polarized illumination light. Asshown in FIG. 20, with TE polarized light and TM polarized light, thereis a difference between the rate of change in measurement errorregarding a change of the inclination angle of the lower face. With themeasurement value of the first measurement condition (TE polarized lightsignals) as M1 and the measurement value of the second measurementcondition (TM polarized light signals) as M2, the true positional offsetamount can be obtained by Expression (10).

The exposure apparatus according to the present embodiment is as shownin FIG. 1, but the alignment detection system 15 differs from thatdescribed in the first embodiment, so the configuration of the alignmentdetection system will be described here. FIG. 21 illustrates theprincipal components of the alignment detection system used in thepresent embodiment. The alignment detection optical system 15 isconfigured of an illumination system 15 i and an imaging system 15 o,wherein illumination light from a light source 18 is enlarged at a lens19 to become parallel rays, split at a polarization beam splitter 36,with the S polarization light (TE polarized light) being reflected at amirror 37, and cast into a polarization beam splitter 39. Also, the Ppolarization light (TM polarized light), which has been transmittedthrough a polarization beam splitter 36 is reflected off of a mirror 38,and is cast into the polarization beam splitter 39. The light joined bythe polarization beam splitter 39 then is collected again at a lens 22.The coherency (σ) of the illumination light is adjusted by a variableopening diaphragm 20. An aperture 23 is disposed at a position conjugatewith the wafer 12, and serves as a view field aperture to preventunnecessary light from being cast on the surrounding areas of thealignment marks on the wafer 12. The light collected by the lens 22 isformed in to parallel rays again at the lens 24, reflected at a beamsplitter 25, passes through a lens 26, and illuminates an alignment mark50 on the wafer 12. The reflected light from the alignment mark 50passes through the lens 26, beam splitter 25, lenses 27 and 28, is splitat a polarization beam splitter 45, and is received at line sensors 32and 34. The aperture (NA) of the imaging system can be adjusted by avariable opening diaphragm 29. The alignment mark 50 is enlarged at animaging magnification of around one hundred times, and the light whichhas been transmitted through the polarization beam splitter 45 is imagedat the line sensor 32 as P polarization light (TM polarized light)signals. On the other hand, the light reflected off of the polarizationbeam splitter 45 is received by the line sensor 34, and can be detectedas S polarization light (TE polarized light) signals.

Note that the method for determining the correction coefficient α andthe AGA (global alignment) method are the same as those with the firstembodiment, and, accordingly, a description thereof will be omittedhere.

Fifth Embodiment

Next, a fifth embodiment of the present invention will be described. Thepresent embodiment is an example of a method wherein two types ofillumination conditions, i.e., broadband light (BB light) with a widewavelength band, and single-wavelength He-Ne beams, are used to changesensitivity regarding non-symmetry of the alignment mark.

FIG. 22 shows the cross-sectional shape model of an alignment mark. Thealignment mark is a model of a case wherein the resist film(P5-P6-P7-P8) on a symmetrical base mark (P1-P2-P3-P4) has becomenon-symmetrical due to irregularities in coating. With regard to a casewherein there is a difference in the inclination angle of the left sideslope (P5-P6) and the right side slope (P7-P8) of the resist, thealignment mark image is simulated and the measurement error ε iscalculated with regard to the broadband light and single-wavelengthsignals using template matching with Expression (3), the results ofwhich are shown in FIG. 23. The conditions of the alignment detectionoptical system are: NA =0.4, σ=0.9, best focus, and TE polarized lightfor the illumination light. The calculation results are for wavelengthsof 633 nm from a He-Ne laser, and broadband light from 580 nm to 680 nm.As shown in FIG. 23, with single-wavelength signals and broadband lightsignals, there is a difference between the rate of change in measurementerror regarding a change of the difference in angle between the left andright slopes of the surface of the resist. With the measurement value ofthe first measurement condition (BB light signals) as M1 and themeasurement value of the second measurement condition (He-Ne wavelengthsignals) as M2, the true positional offset amount can be obtained byExpression (10).

The exposure apparatus according to the present embodiment is as shownin FIG. 1, but the alignment detection system 15 differs from thatdescribed in the first embodiment, so the configuration of the alignmentdetection system will be described here. FIG. 24 illustrates theprincipal components of the alignment detection system used in thepresent embodiment. The alignment detection optical system 15 isconfigured of an illumination system 15 i and an imaging system 15 o,wherein illumination light from a He-Ne laser light source 18 isenlarged at a lens 19 to become parallel rays, and cast into a beamsplitter 42. On the other hand, illumination light from a broadbandlight source 40 is enlarged at a lens 41 to become parallel rays, andcast into the beam splitter 42. Both light fluxes emitted from the lightsources 18 and 40 are joined so as to pass through the same optical pathat the beam splitter 42, and then emitted therefrom and collected at alens 22. The coherency (σ) of the illumination light is adjusted by avariable opening diaphragm 20. An aperture 23 is disposed at a positionconjugate with the wafer 12, and serves as a view field aperture toprevent unnecessary light from being cast on the surrounding areas ofthe alignment marks on the wafer 12. The light collected by the lens 22is formed into parallel rays again at the lens 24, reflected at a beamsplitter 25, passes through a lens 26, and illuminates an alignment mark50 on the wafer 12. The reflected light from the alignment mark 50passes through the lens 26, beam splitter 25, lenses 27 and 28, and isreceived at line sensor 32. The aperture (NA) of the imaging system canbe adjusted by variable opening diaphragm 29. The alignment mark 50 isenlarged at an imaging magnification of around one hundred times, and isimaged at the line sensor 32. Sequentially switching the illuminationlight allows signals from He-Ne laser wavelength and the broadbandlight, to be obtained. While the present embodiment has been describedusing the broadband light and single-wavelength He-Ne laser beams, anarrangement may be made wherein a 488 nm Ar laser is used instead of thebroadband light source shown in FIG. 24 to obtain the two signals fromtwo different light source wavelengths.

Note that the method for determining the correction coefficient cc andthe AGA (global alignment) method are the same as those with the firstembodiment, and, accordingly, a description thereof will be omittedhere.

Now, a description has been made so far regarding different sensitivityto non-symmetry of alignment marks by changing the focus, σ, NA,polarization, wavelength (single-wavelength and broadband light), and soforth, of the alignment measurement conditions. While a description hasbeen made regarding changing the conditions individually, it is clearthat similar advantages can be obtained by using arbitrary combinationsof two or more of these parameters under two measurement conditions.Anyone skilled in the art would be readily able to conceive aconfiguration for such an alignment detection system as a modificationof the alignment detection system described in the presentspecification.

Next, a method for applying wafers from the same semiconductor processto alignment detection optical systems in multiple exposure apparatuseswill be described. In such a case, there is the need to manage themeasurement error TIS (Tool Induced Shift) due to the alignmentdetection optical system. The primary cause of TIS is non-symmetricalaberration of the alignment detection optical system, and, inparticular, coma aberration and telecentricity of the illuminationsystem (the degree of perpendicularity of the primary beam as to thewafer) are major factors. With alignment detection optical systems withgreat TIS, the non-symmetry of alignment marks may expand into greatmeasurement error.

-   Accordingly, in the event of using multiple exposure apparatuses, it    is best to manage the TIS of the alignment detection optical systems    in the exposure apparatuses in the event of using multiple exposure    apparatuses, such that the same non-symmetry error correction    coefficient α is applied for exposure apparatuses having alignment    detection optical systems with TIS within a predetermined threshold    value, and that the correction coefficient α is separately obtained    as described above for exposure apparatuses having alignment    detection optical systems with TIS exceeding the threshold value.

1-8. (canceled)
 9. A position detection method of detecting a position of a mark, said method comprising steps of: detecting light from the mark under a first detecting condition to obtain a position of the mark as a first position; detecting light from the mark under a second detecting condition different from the first detecting condition to obtain a position of the mark as a second position; obtaining previously prepared data for relating a difference between the first and second positions to offset data for offsetting one of the first and second positions; and detecting the position of the mark based on the first and second positions and the previously prepared data.
 10. A position detection method according to claim 9, wherein the previously prepared data is previously prepared from relation between the first and second positions and an error obtained with respect to at least one of the first and second positions.
 11. A position detection method according to claim 9, wherein the previously prepared data is a coefficient to be multiplied to the difference, and one of the first and second positions is offset by a product of the coefficient and the difference, to detect the position of the mark.
 12. A position detection method according to claim 9, wherein the first and second detecting conditions are different from each other in one of focus state of an image of the mark, a coherence factor of an illumination optical system for illuminating the mark, a numerical aperture of an imaging optical system for imaging the mark, a polarization state of light for illuminating the mark, and a wavelength of light for illuminating the mark.
 13. A position detection method of detecting a position of a mark, said method comprising steps of: detecting light from the mark under a first detecting condition to obtain a position of the mark as a first position; detecting light from the mark under a second detecting condition to obtain a position of the mark as a second position; and detecting the position of the mark by weighting the first and second positions with a coefficient and adding the weighted first and second positions, wherein the first and second detecting conditions are different from each other in one of focus state of an image of the mark, a coherence factor of an illumination optical system for illuminating the mark, a numerical aperture of an imaging optical system for imaging the mark, and a polarization state of light for illuminating the mark.
 14. An exposure apparatus for transferring a pattern to a workpiece, said apparatus comprising: means for detecting light from a mark on the workpiece under a first detecting condition to obtain a position of the mark as a first position; means for detecting light from the mark under a second detecting condition different from the first detecting condition to obtain a position of the mark as a second position; means for obtaining previously prepared data for relating a difference between the first and second positions to offset data for offsetting one of the first and second positions; means for detecting the position of the mark based on the first and second positions and the previously prepared data; and means for aligning the workpiece based on the position of the mark detected by said position detecting means.
 15. A method of manufacturing a device, said method comprising steps of: transferring a pattern to a workpiece using an exposure apparatus as defined in claim 14; developing the workpiece to which the pattern has been transferred; and processing the developed workpiece to manufacture the device.
 16. An exposure apparatus for transferring a pattern to a workpiece, said apparatus comprising: means for detecting light from the mark under a first detecting condition to obtain a position of the mark as a first position; means for detecting light from the mark under a second detecting condition to obtain a position of the mark as a second position; means for detecting the position of the mark by weighting the first and second positions with a coefficient and adding the weighted first and second positions; and means for aligning the workpiece based on the position of the mark detected by said position detecting means, wherein the first and second detecting conditions are different from each other in one of focus state of an image of the mark, a coherence factor of an illumination optical system for illuminating the mark, a numerical aperture of an imaging optical system for imaging the mark, and a polarization state of light for illuminating the mark.
 17. A method of manufacturing a device, said method comprising steps of: transferring a pattern to a workpiece using an exposure apparatus as defined in claim 16; developing the workpiece to which the pattern has been transferred; and processing the developed workpiece to manufacture the device. 